Desalination and extraction of high value bio-products from algal-rich seawater using Rhamnolipid as a bio draw solution in forward osmosis

Abstract

In this research, Rhamnolipid has been investigated as a novel bio-draw solution (BDS) for the extraction of high value bio-products and desalination of algal-rich seawater using FO membrane. First, Rhamnolipid was characterized using FTIR, surface tension, osmotic pressure and flux generation analyses. Then, the performance of Rhamnolipid was evaluated and compared with NaCl in terms of microalgae dewatering, seawater desalination and fouling behavior. The results revealed that Rhamnolipid has a high osmotic pressure (up to 29 bar) due to its high diversity of molecular species and solubilization feature. During the microalgae dewatering, water flux of 7.7 and 8.6 LMH were recorded by using 0.2 and 70 g/L of Rhamnolipid and NaCl, respectively. Rhamnolipid showed much less reverse solute flux (∼0.01 GMH) in comparison with NaCl (4.8 GMH). Biomass recovery of 66 % and 48 % was achieved using Rhamnolipid and NaCl, respectively after 60 min FO process. The SEM-EDX analysis revealed that Rhamnolipid leads to less irreversible fouling (13.7 %) than NaCl (26 %). A satisfactory desalination of 99 % was obtained using Rhamnolipid at the optimum concentration of 0.2 g/L. Given to the organic nature of Rhamnolipid the final diluted DS can be utilized as a reuse water for agricultural applications.